Waves

Question 1

What is meant by the amplitude of a wave?

Answer 1

The maximum displacement of a vibrating particle

Question 2

What is meant by the wavelength of a wave?

Answer 2

The least distance between two adjacent vibrating particles with the same displacement and velocity at the same time

Question 3

What is meant by the period of a wave?

Answer 3

The time for one complete wave to pass to a fixed point

Question 4

What is meant by the frequency of a wave?

Answer 4

The number of complete waves passing a point per second

Question 5

What is the equation for the period of a wave

Answer 5

Period = 1/f

Question 6

What is meant by refraction

Answer 6

Change of direction of a wave when it crosses a boundary where it spied changes

Question 7

What is meant by diffraction?

Answer 7

Spreading of waves on passing through a gap

Question 8

State the principle of superposition

Answer 8

When two waves meet, the total displacement at a point is equal to the sum of the individual displacements at that point

Question 9

What is meant by the displacement of a vibrating particle

Answer 9

The distance and direction from the equilibrium position

Question 10

How is a stationary wave formed?

Answer 10

1. Two progressive waves in the same medium
2. Travel in opposite directions
3. With the same wavelength, speed, frequency and amplitude
4. They combine at fixed points to form nodes

Question 11

What is meant by interference?

Answer 11

Formation of points of cancellation and reinforcement where two coherent waves pass through each other

Question 12

What is meant when two sources of waves are coherent

Answer 12

They emit waves with a constant phase difference

Question 13

What machine can be used to demonstrate reflection, refraction, diffraction, interference and polarisation if microwaves?

Answer 13

A microwave transmitter and receiver

Question 14

State and explain advantages associated with a smaller diameter optical fibre core.

Answer 14

1. less multipath dispersion
2. less light is lost
3. better quality signal / less distortion
4. increased probability of TIR
5. Less change of angle between each reflection
6. improved data transfer

Question 15

The red laser light is replaced by a non-laser source emitting white light.
Describe how the appearance of the pattern would change.

Answer 15

• central white (fringe)
• each subsidiary maxima are composed of a spectrum
• AND subsidiary maxima have violet nearest central maximum (OR red furthest from center)
• Fringe spacing less (maxima are wider)

Question 16

Explain the change that occurs when you replace the light to one of a longer wavelength in a double slit

Answer 16

Fringe width,w, increases. Wavelength is proportional to fringe width

Question 17

Explain the change that occurs when you replace the light to one of a longer wavelength in a double slit

Answer 17

Fringe width,w, increases. Wavelength is proportional to fringe width

Question 18

Describe how he should change the way the apparatus is arranged and used in order to obtain an accurate value for the wavelength.

Answer 18

Increase D
when D is increased then w increases
Measure across more than 2 maxima. repeat the reading with a changed distance D

Question 19

explain how the pattern of bright and dark patches is formed

Answer 19

slits act as coherent sources (1)
waves diffract at slits (1)
waves superpose (1)
bright patches : constructive interference as they reinforce each other (1)
dark patches : destructive interference as they cancel out (1)

Question 20

Describe the interference pattern produced by monochromatic light in double slits

Answer 20

1. alternating bright and dark fringes
2. which are equally spaced
3. and have very similar intensity

Question 21

Describe the interference pattern produced by monochromatic light in single slits exper

Answer 21

1. alternating bright and dark fringes
2. bright central maxima
3. decreasing intensity of maxima further away from the central

Question 22

Describe modal dispersion and how it can be prevented (6)

Answer 22

1. Occurs in a wide core
2. Because light travelling along the horizontal axis travels a shorter distance per metre
3. Than light that repeatedly undergoes TIR
4. So a pulse of light sent along a wide core would become longer
5. If it was too long it would merge with the next pulse
6. Therefore use a narrow core

Question 23

When does pulse dispersion occur?

Answer 23

When white light is used instead of monochromatic light

Question 24

Describe material dispersion and how it can be prevented (4)

Answer 24

1. The speed of light in the glass of the optical fibre depends on the wavelength travelling though it
2. The differences in speed of each wavelength in white light
3. Causes violet light to reach the end of the fibre more slowly than red light
4. Monochromatic light must be used to prevent it

Question 25

Describe how the medical endoscope forms an image of a body cavity (5)

Answer 25

1. Contains two bundles of fibre
2. Inserted into a body cavity and illuminated using light
3. A lens over the end of the other fibre bundle is used to form an image of the body cavity
4. The light that forms this image travels along the fibres to the other end of the fibre bundle where the image is observed
   5 this fibre bundle needs to a coherent bundle